The U.S. Food and Drug Administration has approved marketing for a smartphone app claiming to help prevent pregnancy.

Stockholm-based Natural Cycles bills itself as a contraception app leaning on fertility awareness, where a woman tracks the days when she is fertile based on body temperature readings and the timing of her menstrual cycle.

The app requires women who use it to check their temperature daily using a basal body thermometer. The app groups days as either green or red. During red days, users are advised to avoid sex or use protection such as a condom.

"Consumers are increasingly using digital health technologies to inform their everyday health decisions, and this new app can provide an effective method of contraception if it’s used carefully and correctly," said Terri Cornelison, assistant director for the health of women in the FDA’s Center for Devices and Radiological Health, in a statement Friday.

Cornelison also warns despite the high effectiveness rate, Natural Cycles isn't a foolproof solution. "Women should know that no form of contraception works perfectly, so an unplanned pregnancy could still result from correct usage of this device."

Questions have been raised over whether this app is as effective in preventing pregnancy as its makers claim. The U.K.-based Advertising Standards Authority announced in June it was launching an investigation into Natural Cycles after reports women became pregnant while using it, reports the Guardian.

In January, the app faced investigation from Swedish medical authorities after 37 women who used the app became pregnant, reports The Verge.